The invention relates to improvements in apparatus for measuring the density of a tobacco stream, especially in a rod making machine. More particularly, the invention relates to improvements in apparatus which measure the density of successive increments of an advancing tobacco stream by causing one or more beams of radiation to penetrate into the stream and by ascertaining the characteristics (such as the intensity) of radiation which penetrates through the stream.
It is known to measure the density of a tobacco stream with a detector wherein a source of beta rays, visible rays or infrared rays directs one or more beams of radiation against the stream and a suitable transducer serves to generate signals which are indicative of the characteristics of that portion of each beam which has penetrated through the stream. Reference may be had, for example, to commonly owned copending patent applications Ser. Nos. 760,995 and 837,096 of Radzio et al. A drawback of presently known density measuring apparatus of the above outlined character is that the results of measurements are not reliable under any and all circumstances which are likely to be encountered in connection with the density measurement of a tobacco stream in a cigarette rod making or like machine. For example, if the stream exhibits pronounced hills and valleys, the intensity of radiation which penetrates through the stream is likely to reach a value which affects the accuracy of signals from the transducer of the detector. Thus, if the beam of radiation issuing from a source passes through the tobacco stream in a region where the stream exhibits a pronounced depression or valley, the intensity of radiation to which the transducer is exposed can reach a value which entails a distortion of the signal from the transducer to the evaluating circuit so that the signal is not truly indicative of actual density of the respective portion of the stream. The situation is aggravated if the stream of tobacco particles happens to be interrupted so that the entire beam of radiation issuing from the source impinges upon the transducer.
It was further discovered that heretofore known density measuring apparatus do not take into consideration certain other factors which are likely to adversely influence the accuracy of the measurement. For example, such conventional density measuring apparatus do not take into consideration the radiation scattering effect of tobacco particles which are located outside of the actual measuring or monitoring range of the detector, especially of tobacco particles which form the surplus and must be removed in order to convert the stream into a filler which is ready to be draped into a web of cigarette paper or other suitable wrapping material.
Still further, the quality of density measurement can be adversely influenced by localized accumulations of tobacco shreds and/or by fragments of tobacco ribs which find their way into the stream and advance past the density measuring station close to the locus of penetration of radiation into the stream. The transducer of the detector is likely to transmit an inaccurate signal (i.e., a signal which is not truly representative of the density of the corresponding increment of the stream) if the fragments of tobacco ribs and/or accumulations of tightly interlaced tobacco shreds interfere with predictable penetration of radiation through the advancing stream.